Means for maintaining stability of power transmission systems



April 29, 1969 PARK Re. 26,571

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INVENTOR.

ROBERT H. PARK ATTORNEYS R. H. PARK Re. 26,571

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INVENTOR.

ROBERT H. PARK BY M,lmnuq* ATTORNEYS R. H. PARK Re. 26,571

MEANS FOR MAINTAINING STABILITY OF POWER TRANSMISSION SYSTEMS April 29, 1969 /9 ofl9 Sheet Original Filed Aug. 27, 1962 u u nwwu J ,liikK |J n lLl. P'IJ. 3 ML c f l m m T 2 S 3 Y b 6 Y. A l L f E b R o 2 T 3 L U A F M W o f G O 2 3 I. |||ll|||||||Il 6 w INVENTOR. ROBERT H. PARK ATTORNEYS United States Patent Oflice Re. 26,571 Reissued Apr. 29, 1969 Int. Cl. H02j 3/46 US. Cl. 307-86 42 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE Means of increasing the transient stability of power systems in which generating plants, or more broadly in which segments of a system containing generating capacity beyond the need of the segment, are tied to the balance of the system by means of either one line or a plurality of lines which provide parallel paths of power flow, control means, responsive to the occurrence of a line fault, for controlling the driving power of one or more generating segment generator prime movers, in a manner adapted to reduce the driving power on a sustained basis, and for momentarily applying a braking load within the generating segment.

This application is a continuation-in-part of application Serial No. 63,393, filed October 19, 1960, now Patent No. 3,051,842, which application is a continuation-in-part of application Serial No. 848,489, filed October 13, 1959, now abandoned, which application is a continuation-in-part of application Serial No. 769,055, filed October 21, 1958, now abandoned, which application is a continuation-in-part of application Serial No. 582,589, filed May 3, 1956, now abandoned.

This invention relates to power transmission systems and has for its object the provision of reliable and eliicient means for maintaining the electrical stability of such systems subsequent to the occurrence of faults on the lines resulting from insulator flashovers due to lightning, or other causes of a temporary nature.

In power transmission systems a short circuit fault on a line normally operates circuit breakers at each end of the line thereby to isolate the fault, while further after a preset period, chosen long enough normally to extinguish an arc, the breakers may be reciosed automatically.

During the period prior to the opening of the breakers there is a relative acceleration between those synchronous machines within the system which are adjacent to the end of the line that was supplying power prior to the fault and those adjacent to the other end of the line, the relative acceleration being such as to increase the relative angular displacement.

This tendency, moreover, ordinarily continues after the circuit breakers have opened, especially if the line in question represents the sole tie between a generating plant and a receiving system or between two otherwise isolated systems or segments of systems. In this connection, it should be noted that in modern power systems it is common for the receiving segment to include generators as well as loads. Conversely, it is common for the generating segment also to include loads as well as generators. The terms system, as used in the present application, will normally apply where both generating capacity and powerconsuming receivers are contemplated in both the gencrating segment and the receiving segment, although either the generating segment or the receiving segment may, respectively, include only generators and only loads under certain circumstances. The various combinations and permutations to which the invention is applicable are explained in greater detail hereinbelow.

The etiect of such acceleration at one end and of deceleration at the other end is to produce a difference in the velocities and an increase in the relative phase angle between the group of machines adjacent one end of the line, and the group of machines adjacent the other end of the line, with a resultant tendency to loss of synchronism and instability causing voltage disturbances which operate to aifect adversely the performance of connected equipment throughout the system.

Accordingly, it is an object of my invention to reduce to a. minimum such differences in velocities and increases in phase angle.

According to known techniques, design of power transmission systems has been based mainly on the practices of utilizing two or more parallel lines, interconnecting generators, in generating stations, either through low or high voltage busses, connecting parallel lines together at both ends, and also, in the case of long lines, through one or more sectionalizing busses located at intermediate points between the ends and providing high speed switches and relaying adapted to rapidly open the switches at either end of a line or section of line that has become faulted thereby to isolate the fault, while also it is often the practice to reclose the same breakers after a short interval during which the are at the point of fault may be expected to have become extinguished.

Published theoretical studies have been carried out relative to the advantages which can be realized through use of relaying and circuit breakers adapted to rapidly open the breakers at both ends of a single transmission line connecting generators in a generating station to a load center thereby decoupling the generating station from the load center, and then, after a brief interval, reclosing these breakers.

These studies have shown that, in this single line case, use of the principle of rapid reclosing will often result in instability, when the load on the generators exceeds a critical value less than full load, even when the highest practicable speed of reclosing is utilized.

One phase of my invention relates to the procedure in conjunction with such single line transmission and automatic reclosing, of, in the event of a line fault, promptly isolating the fault and applying a resistive breaking load to the generator or generators feeding the line, and disconnecting this load, preferably at or about the time that the line breakers reclose, and constitutes an improvement over procedures heretofore described.

In another phase of this form of my invention, means are employed whereby the driving force applied to the moving element of the generator prime mover or prime movers is rapidly reduced on the occurrence of a line fault and thereafter rapidly restored at or about the time the line breakers reclose.

Another object of my invention is to make practicable the use of single line in place of double line transmission systems, with a resultant saving in capital cost.

Another object of my invention is to allow use of longer and lower voltage single line transmission systems than would otherwise be practicable.

Another object of my invention is to allow full generating station power transmission over one of two parallel lines without danger of instability in the event of a line fault when the other lines is out of service due to need for repairs or for other reason.

Another object of my invention is to allow the stable transmission of power generated by two or more genera- 

